Solid state ring laser

ABSTRACT

A solid state one-piece ring laser having a plurality of surfaces for converting broad band light to a ring laser beam. At least one surface is refractive and is arranged at a Brewster&#39;&#39;s angle to the ring laser beam to linearly polarize the ring laser beam. Some of the surfaces may be reflective and are arranged at critical angles to the ring laser beam. With this arrangement, none of the surfaces needs to be coated with a dielectric which deteriorates with age and environment. In a preferred arrangement, as many of the surfaces as possible are refractive to provide a more coherent laser beam.

[15] 3,657,733 [451 Apr. 18,1972

[54] SOLID STATE RING LASER [72] Inventors: William A. Shapiro,l-lackensack, N.J.; Robert P. Kemmerer, Jr.,' Bloomington,

Calif.

[73] Assignee: The Bendix Corporation [22] Filed: Aug. 25, 1969 [21]Appl. No.: 852,708

[52] US. CL; ..330/4.3, 331/945, 350/152 [51] Int. Cl..... ..Il0ls 3/02,H01s 3/05 [58] Field ofSearch ..33l/57,94.5;350/152;

[56] References Cited UNlTED STATES PATENTS Sorokin ..33 l/94.53,414,839 12/1968 Briges et al. 3,462,708 8/1969 McClure 3,504,3003/1970 Mazelsky FOREIGN PATENTS OR APPLICATIONS 1,128,162 9/1968 England..331/ 94.5

1,388,843 1/1965 France ..33l/94.5

OTHER PUBLICATIONS Applied Physics Letters, May 1, 1968 Vol. 12, No. 9by J. E. Geusic et al. Continuous 532-n Solid State Source Using PrimaryExaminer-Richard A. Farley Assistant Examiner-N. MoskowitzAttorney-Ronald G. Gillespie and Plante, Hartz, Smith and Thompson [57]ABSTRACT A solid state one-piece ring laser having a plurality ofsurfaces for converting broad band light to a ring laser beam. At leastone surface is refractive and is arranged at a Brewster's angle to thering laser beam to linearly polarize the ring laser beam. Some of thesurfaces may be reflective and. are arranged at critical angles to thering laserbeam. With this arrangement, none of the surfaces needs to becoated with a dielectric which deteriorates with age and environment. Ina preferred arrangement, as many of the surfaces as possible arerefractive to provide a more coherent laser beam.

2 Claims, 2 Drawing Figures LIGHT SOURCE Patented April 18, 19723,657,733

2 Sheets-Sheet l LIGHT SOURCE RING LASER BEAM 4 a LASER l LASER BEAM 7/BEAM -7A W I DETECTOR L IIA EIA 1 INVENTORS W/LL [4M A. SHAP/IQOROBE/QT P KEMMERERJR HI'I'OR/VEY Patented April 18, 1972 2 Sheets-Sheet2 BROAD BAN D LIGHT 2 RING LASER y/BEAM 3| LAsEii BEAM a2 FIG: 2

INVENTORS W/LL/AM A SHAP/RO ROBERT P A EMMERER JR WMJQQ 5. 5

ATOR/VEY soul) STATE RING LASER BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates to lasers and, moreparticularly, to solid state ring lasers.

2. Description of the Prior Art Heretofore, ring lasers were constructedwith gas filled tubes and with mirrors, which had to be accuratelyaligned. The laser had to be rugged for airborne use and this added bulkand weight which made its use impractical.

A toroidal solid state ring laser is disclosed in Laser OperationWithout Spikes in a Ruby Ring, by Peter Walsh and G. Kemeny, at page 956of Volume 34, number 4 of the April, 1963 issue of Journal of AppliedPhysics. The toroidal ring laser overcomes the problems of the gas usingring lasers but provides a laser beam which is not highly coherent andrequires dielectric coatings on the reflective surfaces whichdeteriorate with age and temperature change. Furthermore, the toroidalring laser does not linearly polarize the laser beam.

SUMMARY OF THE INVENTION A solid state ring laser responsive tobroadband light to provide a highly coherent linearly polarized laserbeam, comprising a body of lasing material having a plurality ofsurfaces arranged to convert the broadband light to a ring laser beam.At least one surface is refractive to linearly polarize the ring laserbeam and one of the surfaces is partially reflective and partiallyrefractive to convert the ring laser beam to a laser beam.

One object of the present invention is to provide a ring laser providinglinearly polarized laser beams.

Another object of the invention is to providea solid state one-piecering laser which is economical and rugged.

Another object is to arrange refractive surfaces at Brewsters angle tothe beam and reflective surfaces substantially at the critical angle toavoid coating the surfaces with a dielectric which deteriorates andcauses unsatisfactory operation.

The aforegoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingswherein two embodiments of the invention are illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for illustration purposes only and are not to be construed asdefining the limits of the invention. 1

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a laser system constructed inaccordance with the present invention using a solid state one-piece ringlaser in which substantially all the light coherent surfaces arerefractive.

FIG. 2 shows a second embodiment of the invention which includes onlytwo refractive surfaces.

DESCRIPTION OF THE INVENTION Referring to FIG. 1 there is shown a lasersystem having a light source 1, such as a xenon tube, which transmitsbroad band light 2 to a solid state one-piece ring laser 3, constructedaccording to the invention to provide a bi-directional, as indicated bythe arrows, ring laser beam 4.

Ring laser beam 4 is converted to laser beams 7, 7A which may be useddirectly in any conventional manner or may be applied to a detector 9 toprovide alternating current voltages E and E at output terminals 11 and11A, respectively, which may correspond to rotation rates of the ringlaser as described in US. Pat. No. 3,320,850.

Ring laser 3 comprises a body in which the active medium preferably isruby although other material such as neodymium glass and neodymiumyttrium aluminum garnet may be used. The active medium determines thewave length of the ring laser beam. The refractive index of the activemedium determines the minimum number of lasering legs and the number ofrefractive and reflective surfaces necessary to provide the ring laserbeam.

Using ruby as the active medium, the ring laser beam 4 will have a wavelength of 6,943 A. and ring laser 3 has refractive surfaces 15 to 22 anda partially reflective surface 23 which directs light of this wavelength in a closed path, as indicated by the dotted line of ring laserbeam 4, in opposite directions. The portion of internal radiation,caused by light 2, following the closed path is continually reinforcedby subsequent radia tion to provide a ring laser beam 4. The remainderof the internal radiation that does not follow the closed path isdissipated in laser 3.

Surfaces 16, 18 and 20 are arranged at an angle of 59 12 to surfaces 17,19 and 21 so that the angle of incidence of ring laser beam 4 to thosesurfaces is at Brewsters angle 0 of 60 24' from air to ruby and 0, of 2936 from ruby to air. The use of Brewsters angles avoids the use ofdielectric coatings on the surfaces.

Brewsters angles are determined by the refractive indicies of thedifferent mediums and the wave length of the ring laser beam. In thepresent arrangement the refractive index of ruby at the lasing wavelength of 6,439 A. is approximately 1.76 and the refractive index forair is approximately 1 so that the Brewsters angle from air to ruby is60 24' as indicated above. The Brewsters angle from ruby to air is 2936'.

As ring laser beam 4 is refracted at the Brewsters angle from one mediumto another, it is linearly polarized and the number of times ring laserbeam 4 is refracted determines the extent of linear polarization of ringlaser beam 4.

A highly linearly polarized laser beam is especially desirable inholography and as a rotation rate detector.

Surfaces l5 and 22 are arranged at an angle 0;, of 121 I656 to surfaces16 and 21, respectively, so that ring laser beam 4 strikes surfaces 15and 22 at near Brewsters angle 0 of 29 46' from ruby to air and 0 of 6052% from air to ruby. Surfaces 15 and 23 and surfaces 22 and 23 arearranged at an angle 0 of 64 18% so that the angle of incidence of laserbeam 4 to surface 23 is at an angle 0 of 34 32% which is substantiallythe critical angle. This provides a high degree of reflection withoutthe use of dielectric coating and permits a small portion of ring laserbeam 4 to be refracted at an angle 0 of 86 16 to detector 9.

The laser system shown in FIG. 2 is similar to the laser system shown inFIG. 1 except that a ring laser 30, which receives broad band light 2from light source 1 and provides a ring laser beam 31, has tworefractive surfaces 33 and 38 and a partially reflective surface 39, thelatter surface also refracting a portion of ring laser beam 31 todetector 9. Reflective surfaces 33 and 38 of laser 30 are arranged at anangle 0 of 75 36' to refractive surfaces 35 and 36, respectively, sothat the angle of incidence of ring laser beam 31 to surfaces 34, 36 isat a Brewsters angle 0 of 60 24' from air to ruby and 6 of 29 36' fromruby to air, and the angle of incidence of ring laser beam 31 toreflective surfaces 33 and 38 is at a critical angle 0 of 45.

Partially reflective surface 39 preferably has a dielectric coating toincrease the reflectivity of the surface so that approximately percentof ring laser beam 31 is reflected and the remainder is refracted bysurface 39 at an angle 0 of 56 to provide linearly polarized laser beams32 and 32A which may be used in a conventional manner.

The one-piece solid state ring laser constructed according to theinvention is economical and rugged and provides a linearly polarizedlaser beam. The refractive surfaces arranged at Brewsters angles and thereflective surfaces arranged at substantially the critical angle avoidcoating the surfaces with the dielectric to improve operation andincrease the life of the ring laser.

While two embodiments of the invention have been illustrated anddescribed in detail, it is to be expressly understood that the inventionis not limited thereto. Various changes may also be made in the designand arrangement of the parts without departing from the spirit and scopeof the invention as the same will now be understood by those skilled inthe art.

What is claimed is:

l. A solid state ring laser responsive to broad band light and providinga linearly polarized laser beam, comprising:

a body of lasing material having a plurality of surfaces arranged toconvert the broad band light to a ring laser beam;

the plurality of surfaces including four pairs of adjacent refractivesurfaces for linearly polarizing the ring laser beam; and

one of the surfaces being partially reflective and partially refractiveto convert the ring laser beam into a laser V providing a linearlypolarized laser beam comprising:

a body of lasing material having a plurality of surfaces arranged toconvert broad band light to a ring laser beam; the plurality of surfacesincluding one pair of adjacent refractive surfaces for linearlypolarizing the ring laser beam and two reflective surfaces arranged atcritical angles to the ring laser beam to achieve a high degree ofreflectivity without the use of a dielectric coating; and

one of the surfaces being partially reflective and partially refractiveto convert the ring laser beam into a laser beam.

1. A solid state ring laser responsive to broad band light and providinga linearly polarized laser beam, comprising: a body of lasing materialhaving a plurality of surfaces arranged to convert the broad band lightto a ring laser beam; the plurality of surfaces including four pairs ofadjacent refractive surfaces for linearly polarizing the ring laserbeam; and one of the surfaces being partially reflective and partiallyrefractive to convert the ring laser beam into a laser beam.
 2. A solidstate ring laser responsive to broad band light and providing a linearlypolarized laser beam comprising: a body of lasing material having aplurality of surfaces arranged to convert broad band light to a ringlaser beam; the plurality of surfaces including one pair of adjacentrefractive surfaces for linearly polarizing the ring laser beam and tworeflective surfaces arranged at critical angles to the ring laser beamto achieve a high degree of reflectivity without the use of a dielectriccoating; and one of the surfaces being partially reflective andpartially refractive to convert the ring laser beam into a laser beam.